A graphic display apparatus basically comprises a display screen, display controller, data channels and some input devices.
There are many types of input devices one of which is an X-Y direction input device called "MOUSE" (tradename) configured to detect the moving direction and distance of a casing on a base.
The X-Y direction input device basically comprises a rotatably supported ball made of steel, for example, a first follower roller contacting and rotated by the ball, a second follower roller contacting and rotated by the ball and having an axis perpendicular to the axis of the first follower roller, first and second rotation detectors each including rotary electrical members such as variable resistor and encoder to separately detect rotations of the first and second follower rollers, and a casing which receives and envelopes the ball, first and second follower rollers, first and second rotation detectors and other related members.
Normally, such an X-Y direction input device further comprises push switches located inside the casing to effect deletion or dislocation of patterns displayed on the screen or to effect various signal processing for other switching and control operations when activated through switch operating members exposed outside the casing for manual compression.
The casing has an aperture which opens at the bottom thereof to allow the ball to slightly project downward. When the casing is moved, rotating the ball on the base, the first and second follower rollers are rotated in predetermined different (X- and Y-) directions respectively. The directions and amounts of rotations of the first and second follower rollers are extracted by the first and second rotation detectors separately, as corresponding voltages or digital signals of X- and Y-directional components, and the signals are entered in the display apparatus.
In the prior art X-Y direction input device, the reference axes of the coordinate system are fixed by positions of the first and second follower rollers with respect to the casing. For example, if the first follower roller for detection of an X-direction component is disposed parallel to the length direction of the casing whereas the second follower roller for detection of a Y-direction component is disposed perpendicular to the second follower roller, the coordinate system of the input device is absolutely fixed, with the shorter margin (width) of the casing being the X-axis and the longer margin (length) of the casing being the Y-axis. Therefore, a user has to grip or pinch the input device so that the length direction thereof extends accurately longitudinally with respect to his body, when he moves it to effect a desired input operation.
However, the best holding angle of the input device varies with users. For example, it will be more convenient for some users to incline the input device by an angle with respect to his body. It will often occur for these users that although he intended to move the input device longitudinally, i.e. in the Y-axis direction, in the attempt to move the cursor in the Y-axis direction on the screen, the cursor actually moved in an inclined direction. This is because the actual moving direction of the user's hand does not coincide with the length direction of the casing, i.e. the Y-axis direction of the input device.
This also applies to an X-Y direction input device called "TRACKBALL" type where a casing is put on a desk or other base member, with a ball being exposed above the casing for manual rotating operation. The "TRACKBALL" type input device will similarly cause a deviation between the coordinate axes in the user's mind and the coordinate axes of the input device if the user puts the input device on the desk, with its coordinate axes being deviated from user's intended coordinate axes.
Additionally, as to switch activating members provided on the casing for manual compression to instruct a desired signal processing, their best positions vary with users.